This invention deals with an innovative apparatus and method to control the tension of one or more additional yarns utilized in the weaving of fabric and more particularly in the selvage of a woven fabric.
It is common in the weaving art to add additional yarns into the selvage area of fabric for a variety of reasons. It is common when there are more than a few yarns involved, that they be wound together onto a spool type device. This spool is then mounted on the weaving machine, thus allowing the yarns to be fed into the weaving process. To provide yarn tension to facilitate the weaving process, resistance to the rotation of the spool is provided typically by a strap loaded by a spring and wrapped around or near the perimeter of the spool. For example, a conventional selvage yarn tensioning device may include one or two circumferential straps which are spring biased against a constant diameter portion of the spool (spool edge) and there may be a traveling roller which contacts the yarn on the spool and which provides for a reduction in the spring tension as the effective diameter of the yarn remaining on the spool decreases. Such a roller is supported, for example, by one end of a lever arm which pivots about a shaft which also serves as an anchor for one end of each of the tensioning straps.
Since the amount of torque acting on the spool caused by the drag of the strap or straps would at best be relatively constant, the tension on the yarns would vary as the diameter of the yarns on the spool winds down. Mechanical devices have been added, such as, a wheel assembly which rides on the yarn in the spool and is connected through a lever in order to change the spring loading in an attempt to compensate for the change in diameter.
Such a conventional tensioning apparatus is shown in FIGS. 1 and 2. These schemes do not fully compensate for the diameter change effect, wear on the strap or spring, or differences in the coefficient of friction between multiple straps or spools. Also, it is difficult for machine operators to properly adjust the tension as the spring and straps wear, as the yarn is fed off of the spool, for different types of yarn, and the like.
Since the selvage yarn tension can not be properly maintained using conventional means, it is typical for machine operators to constantly monitor and adjust the selvage yarn tensioning devices in an attempt to maintain a constant tension on the selvage yarn. Hence, there exists a need for an improved selvage yarn tensioning apparatus and method.
In accordance with the present invention there is provided a simple and economical mechanical device that automatically adjusts the tension applied to the strap or other means used to brake the yarn spool such that the tension of the selvage yarn remains constant as the diameter of the yarn wound on the spool changes.
Also, provision is made for more consistent fabric properties due to increased consistency of the yarn woven into the selvage that influences filling crimp during weaving. Still further, there is provided a reduction in the amount of time spent by weaving personnel needed to adjust the selvage tensioning mechanism within the tolerance of yarn tension required to achieve desired fabric properties.